The present invention refers to a method for the complete, dry desulphurization of combustion flue gases comprising SO.sub.2 and particles, as well as to an apparatus for carrying out the method.
The method especially refers to the complete and dry desulphurization of combustion flue gases of the combustion of coal, in particular the combustion of brown coal, in which fly ash is comprised in the combustion flue gas.
The method further refers to the desulphurization of SO.sub.2 containing combustion flue gases of other combustibles which instead of fly ash contain particles which have comparable properties described below.
Dry desulphurization means that the desulphurization process takes place at such a temperature distance from the dew point of the combustion flue gases, that the equipment portions downstream of a combustor (dedusting equipment, chimney) can be operated without any occurrence of condensation.
For the complete desulphurization, only wet methods are known, in which the combustion flue gases are brought into contact with absorbing liquids, such as caustic potash solution. It is disadvantageous, however, that the combustion flue gases leave this step of the process completely or almost completely moistly saturated, which results in caking and corrosion of the downstream equipment portions, attempts being then made to eliminate such results by re-heating the combustion flue gases.
Dry desulphurization methods are also known, in which for example CaCO.sub.3 is blown into the combustion chamber. It decays at approximately 900.degree. C. to become CaO, which then partly reacts with SO.sub.2 and SO.sub.3. In this manner, desulphurization degrees of slightly above 80% could be achieved but not a complete desulphurization.
Desulphurization methods, in which the combustion flue gases together with fly ash and/or added absorbentia are cooled down to almost the dew point of the combustion flue gases, or in which the dew point is raised by adding water or steam, come closer to this object, see for example DE 32 40 373 or DE 33 32 928. There, especially the last portion of the cooling process of the smoke gases is effected by previously adding other cooled-off fly ash and/or absorbentia to the combustion flue gas, to cool it further down thereby. Therein, it is desired to achieve the cooling-down to less than 5.degree. C. above the dew point, since only then desulphurization degrees of 90% and more could be achieved. A complete desulphurization by that method is not known up to now.
Another dry operating desulphurization method is described in the magazine ZKG 3/1990, pages 139-143. There, the SO.sub.2 comprising combustion flue gases are passed through a fluid bed, which consists of Ca(OH).sub.2 and cement raw powder. The fluid bed is operated in close proximity of the dew point of water, especially at an operation temperature of about 65.degree. C. with a dew point of between 58.degree. and 61.degree. C. Despite the high cost of equipment, energy and absorbentia consumption, the desulphurization is only achieved to a SO.sub.2 contents of 423 mg/mn.sup.3. It is further disadvantageous that the proximity to the dew point causes cakings, and that the remaining SO.sub.2 contents results in corrosions of the downstream portions of the equipment. By means of a further decrease in the distance to the dew point, which in this cases is only about 65.degree.-61.degree.=4.degree. C., the desulphurization can be slightly improved, however the problems concerning caking and corrosion are increasing. A complete and dry desulphurization by means of this method is also impossible.